Ordinary spark-ignition internal combustion engines utilize a carburetor/intake manifold combination as part of their fuel system. In the carburetor, air and fuel are blended and fed into the intake manifold for distribution to the cylinder or cylinders. In order to ensure good engine operation, the air:fuel mixture is kept near and usually slightly higher than the stoichiometric ratio. The use of such rich fuel:air mixtures contributes to undesirable unburned hydrocarbon and carbon monoxide exhaust emissions. Operating an engine using air:fuel mixtures greater than stoichiometric, commonly called a lean mixture, will result in reduction of exhaust hydrocarbon emissions. The ordinary carburetor, however, although capable of providing lean mixtures, is inadequate because (1) it cannot provide these lean mixtures for all engine operating conditions, (2) its fuel/air mixing capability is relatively poor for lean mixtures, and (3) it is ordinarily limited to providing fuel/air ratios down to only about 1:15.5. There are carburetors available, (e.g. Delco-Rochester's "Quadra Jet"; also, see U.S. Pat. No. 3,310,045, to E. Bartholomew) which do effect good air/fuel mixing at relatively lean air/fuel ratios. However, such carburetors are somewhat limited in their capacity to provide sufficient air/fuel mixture for high engine demand; these carburetors are relatively complex in structure; and finally, their air/fuel blending characteristics for lean mixtures, for example, air/fuel of 18:1 and higher, may not be adequate for good engine performance. These carburetor limitations in general have an adverse effect on the driveability of an automobile -- especially where the engine is equipped with other exhaust emission reducing modifications such as catalytic converters, thermal reactors, etc.
The present invention provides a carburetor of novel design and relatively simple construction featuring a combination of at least one primary barrel of conventional venturi construction and at least one secondary barrel having a cross-sectional area larger than the first barrel and having means whereby the cross sectional area can be varied in response to engine demand. This carburetor affects excellent air/fuel mixing over a wide range of air:fuel ratios, especially in the leaner air:fuel ratios, i.e. 16:1 - 18:1. The variable cross sectional area secondary barrel feature provides sufficient capacity for the carburetor to ensure adequate air:fuel supply to be provided to an engine even a high engine demand. Use of the carburetor of the present invention on a conventional internal combustion engine improves the efficiency of such an engine and reduces undesirable exhaust emissions, especially the hydrocarbons and carbon monoxide. Furthermore, when the present carburetor is used in place of currently available carburetors, with an engine which is modified to further decrease exhaust emissions, for example, with a catalytic converter or a lean reactor system, the driveability of an automobile powered with this new combination is significantly improved.